How a steam-water-oil heat exchanger protects fuel systems

Did the system for warming warship fuel oil pass steam directly through the oil tank?

Probably not directly; the described arrangement used steam to heat water, which then heated the oil so a steam-pipe failure could not contaminate the fuel.

The answer recalls a two-stage exchanger in which steam heats water and the water then warms the fuel oil. Keeping steam piping away from the oil reduces the risk that corrosion or a pipe failure will contaminate fuel with water. That separation matters because heavy ship fuel is already difficult to handle and water contamination can make it unusable for the machinery. It presents the exact arrangement from memory and notes that a diagram would be needed for a definitive component-level explanation.